| Abstrakt: |
The proteolytic activities of normal, Schmidt Ruppin Rous sarcoma virus (SR-RSV transformed, and infected (RAV) chick embryo fibroblasts (CEF) have been measured by a highly sensitive technique using 3H-acetylated haemoglobin as a substrate. When all 3 types of CEF cells were maintained in serumless media, no differences were detected in the amount of pH 3·4 protease activity released into the media over a 24–h period, and only negligible amounts of pH 7·6 proteolytic activity were found. When normal, transformed, and infected cells were maintained in serumless media and later incubated with 3H-acetylated haemoglobin, a significant proteolysis of the haemoglobin, a 6-fold increase compared to the normal CEF cells, was associated only with plates containing SR–RSV–CEF cells. A fluorescent assay for peptides confirmed that SR–RSV–CEF cells have increased cell-associated proteolytic activity. The net surface charge of the transformed CEF cells was unchanged by maintenance in serumless media but the net surface negativity of the normal and RAV-CEF cells was significantly increased by incubation in media minus serum for 24 h. This suggests that normal CEF cells, maintained in media plus serum, have a substance masking their surface charge which is absent from the surface of transformed cells, possibly because of proteolytic degradation. |
